A process for the preparation of a polymerizable unit for production of a hole transporting polymer for use in an optical device, which process comprises reacting in the presence of S to form wherein each R is the same or different and is independently H or a substituent group; n is O or an integer from 1 to 100; Ar and Ar′ are the same or different and are each aromatic or heteroaromatic groups which are substituted or unsubstituted; Y is a direct bond, a light emissive moiety, a hole transporting moiety or an electron transporting moiety; and X is a polymerizable group.